v0.0.17

• Fixes #34, add colspan and rowspan to the list of allowed attributes;
• Adds filename, beforeToc and excludeFromToc options to content definition object;
• Fixes #27, doesn't create a empty images folder when book has none to prevent validation issues;

Known issues

• Do not use this version, please upgrade/use v0.0.18. There seems to be an issue with images download with this version, where no image is downloaded;